1. Field of the Invention
The present invention relates to image processing for generating code information by encoding information into a regular sequence of a pixel cluster.
2. Description of the Related Art
An information description method for printing code information that requires some decoding processing for source information in place of readable information such as text or the like, the contents of which can be easily recognized, is prevailing. A representative example of such code information is a two-dimensional code like a QR code®.
An application program or the like, which runs on a computer, normally encodes source information such as text or the like, and sends code information to a printer, thus printing the code information on a print medium such as paper sheet or the like.
The contents of the printed code information cannot be recognized intact. However, when the code information is scanned as an image using a scanner, and that image undergoes decoding processing, readable information can be obtained. An application program which runs on a computer performs the decoding processing by inputting the scanned image to the computer. Alternatively, for example, a decoder like a portable phone that supports the two-dimensional code or a multi-functional peripheral equipment (MFP) having a scanning device such as a scanner or the like may decode the image.
The two-dimensional code (code information by encoding information into a regular sequence of a pixel cluster) generally has an information area as a minimum unit that forms the code (to be referred to as “cell” hereinafter). By arranging two types of cells which are defined in advance according to rules defined in advance, readable information is encoded. Normally, the two types of cells include a black cell that prints black, and a white cell that prints nothing. Therefore, when the data size of source information to be encoded (to be referred to as a “source information size” hereinafter) is large, the number of cells increases accordingly, and the data size of the encoded information (to be referred to as a “code size” hereinafter) becomes large.
Upon printing code information on a print medium as a two-dimensional code, each cell is formed as a pixel cluster including a predetermined number of pixels. In this case, if the source information size remains the same, the code size increases with increasing number of pixels per cell, i.e., with increasing cell size. That is, the final code size is influenced by two factors, i.e., the source information size and the cell size. Note that the source information often includes additional information (error correction code or the like) required in the process of encoding the source information and in the process of decoding in addition to the source information itself.
Also, as is known, slight dot fattening and thickening in an output device greatly influences the recognition precision of the code information. In consideration of recognition of code information by an MFP, code information which is appended to printed matter by the MFP must be analyzed by the MFP. Hence, the code information must be generated based on generation parameters (a cell size, cell shape, error correction amount, and the like) which consider copy degradation resistance of the MFP itself, and the generated code information must be embedded in the sheet surface. Note that the copy degradation resistance refers to resistance that allows decoding code information even using a second generation copy formed by repeated copying.
However, the print characteristics of the MFP vary depending on individual differences, environmental changes, aging, and the like. Such characteristic variations greatly influence the recognition precision of the code information, and the high recognition precision of the code information appended to printed matter by the MFP cannot often be guaranteed.
As a technique for suppressing the characteristic variations of the MFP, calibration is well-known. The calibration is a technique in which the MFP outputs a test chart, and scans it. Color differences are calculated between the data of the scanning result and those of the test chart, thus correcting image processing conditions and supply signals of color materials (toners or inks) (for example, see Japanese Patent Application Laid-Open No. 9-185209).
However, the calibration is a technique for correcting an image itself, but it does not guarantee recognition precision by correcting the generation method and appending method of code information to be appended to printed matter. For this reason, the cell size as a dominant generation parameter for improving the copy degradation resistance has a large margin, and code information such as a two-dimensional code is printed.
However, when the cell size has a large margin, the following problems are posed: the code size increases, printing of code information with a large cell size makes the printed matter unsatisfactory to the viewer, the degree of freedom in layout of code information deteriorates, and so forth.